Sewing machine drive mechanism



Aug. 6, 1968 F. e. CRETER SEWING MACHINE DRIVE MECHANISM Filed March 24; 1965 INVENTOR. Frederick G. Crefer WITNESS Wham 9k TORNE Y United States Patent 3,395,661 SEWING MACHINE DRIVE MECHANISM Frederick G. Creter, Bricktown, N.J., assignor to The Singer Company, New York, N.Y., a corporation of New Jersey Filed Mar. 24, 1965, Ser. No. 442,268 2 Claims. (Cl. 112-220) ABSTRACT 0F THE DISCLOSURE An improvement in the low speed work-penetrating characteristics of a sewing machine having a coil spring power transmission member. The improvement consists in placing a resilient annular abutment member within the coil spring so as to allow a small clearance bet-ween the abutment member and the coil spring. As torque is applied to the coil spring, it will flex to a small uninhibited deflection after which further flexing is resisted by the annular abutment member.

This invention relates to sewing machines of the type adapted to be gear driven from an electric motor, having included in the drive a spring power transmission member and, more particularly, to a novel means for improving the low speed work penetrating characteristics of such sewing machines.

While the work penetrating characteristics of a sewing machine might be enhanced by the use of a more powerful drive motor, this solution to the problem of increasing work penetrating ability presents serious drawbacks in that appreciable added expense is involved, the corresponding increase in size and weight of a larger motor presents support and housing problems, and an increase in overall drive power may require a general redesign of the entire actuating mechanism of the sewing machine.

It is an object of this invention to provide for a substantial increase in the low speed work-penetrating characteristics of a sewing machine having a spring power transmission member, by providing an annular abutment member within said transmission member to limit the flexing of said spring power transmission member.

It is a further object of this invention to provide an annular abutment member within a spring power transmission member in a sewing machine of the above character wherein said abutment member is extremely simple in construction so as to be readily adapted for use on sewing machines not originally built to include this feature.

Having in mind the above and other objects that will be evident from an understanding of this disclosure, the invention comprises the devices, combinations and ar rangements of parts as illustrated in the presently preferred embodiment of the invention which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation, construction and advantages of it when read in conjunction with the accompanying drawings in which:

FIG. 1 is a vertical cross-sectional view taken through a portion of a family type sewing machine embodying the present invention.

FIG. 2 is a cross-sectional view taken substantially on the line 22 of FIG. 1.

FIG. 3 is an exploded perspective view of the parts illustrated in FIGS. 1 and 2.

Referring to FIG. 1 of the drawings, 11 indicates a fragment of the frame of a sewing machine sustaining a bushing 12 in which is journaled a sewing machine drive shaft 13. It will be understood that the drive shaft 13 is a portion of the actuating mechanism of the sewing machine and turning movement imparted to the shaft 13 will drive the stitch forming and work manipulating instrumentalities "ice (not shown) of the sewing machine in a conventional manner.

An electric drive motor 14 for the sewing machine is carried preferably in the sewing machine frame and includes a motor shaft 15 formed with a worm 16. The worm 16 meshes with a worm wheel 17 which is freely journaled on a bearing surface 18 formed on a shaft collar 19 secured by a screw 20 on the drive shaft 13. Disposed on the sewing machine drive shaft 13 adjacent to the worm wheel 17 is a handwheel 21 which is made part of the drive shaft by a shouldered screw 22 threaded into the drive shaft. The handwheel is framed with an annular recess 23 in the face contiguous to the worm Wheel 17, the recess 23 defining an outer axial flange 24 and an inner axial flange 25. The handwheel may in addition be formed with various cavities and reinforcing ribs 26 and 27 to facilitate manufacture as by moulding of plastic material, however such additional features of the handwheel construction do not form a direct part of this invention which may be used as well with any conventional handwheel construction.

The worm wheel 17 is not connected directly to the sewing machine drive shaft 13 but instead is connected thereto by way of a coil spring 30 which is disposed in the handwheel recess 23 and coiled about the drive shaft 13. One axially offset extremity 31 of the coil spring extends through a hole 32 formed in the worm wheel 17 while the opposite axially offset extremity 33 of the coil spring enters a hole 34 formed in one of the reinforcing ribs 26 of the handwheel. The coil spring 30 serves to minimize gear noise and has been found to prolong gear life by cushioning the variation of gear load which arise during normal operation of a sewing machine.

While the use of a spring such as the coil spring 30 between the worm wheel 17 and the drive shaft 13 has been found to be highly desirable in reducing gear noise and prolonging gear life, these advantages have heretofore been realized at the expense of a considerable reduction in work penetrating ability of the sewing machine needle. During work penetration, the coils of the spring power transmission element 30 wind, and in so doing reduce the gear noise and prolong the gear life. This winding of the coil spring, however, gradually slows the electric motor and reduces the effective kinetic energy existing in the electric motor and available to drive the needle. Such loss of kinetic energy and accompanying reduction in maximum available torque can prevent work penetration of thick fabrics.

The present invention provides a means for retaining the beneficial reduction of gear noise and prolonged gear life provided by the coil spring 30 while at the same time so limiting the maximum possible flexing of the spring as to provide substantially optimum work penetrating characteristics.

To this end an annular, preferably non-metallic abutment member 40 is disposed within the annular recess 23 of the handwheel and within the coils of the coil spring 30. An axial aperture 41 in the annular member 40 is seated snuggly on the inner radial flange or hub 25 of the handwheel and the exterior peripheral surface 42 of the annular member 40 fits with slight clearance within the unflexed coils of the coil spring 30.

When a torque is applied to the coil spring 30, therefore, an initial uninhibited flexing of the spring is possible during which the diameter of the spring coils reduce in diameter as the torque increases. This has been found suflicient to provide optimum reduction in gear noise and prolonged gear life. Additional flexing of the coil spring 30, however, is limited by the annular abutment member 40 since the external surface 42 will prevent further deflection of the spring once contacted by the spring as the spring coils reduce in diameter upon the application of increased torque.

Limiting deflection of the spring by providing a resilient annular member within the coil spring has been found to substantially increase the life of the spring and of the abutment member, and to provide a particularly durable construction. The annular abutment member of the present mechanism limits spring deflection by distributing a resisting force radially about the entire internal surface of the spring. This resisting force is not localized, and therefore, cannot give rise to excessive stress and wear at any one portion of the spring or at any one portion of the abutment member. It has been found that the initial uninhibited flexing of the spring serves in reducing gear noise and prolonging gear life as effectively as complete spring flexing. By limiting the spring deformation to a small initial uninhibited flexing however, the annular member makes the spring act as though it were a rigid connection between the worm wheel 17 and the drive shaft 13 so that substantially the maximum kinetic energy present in the electric motor drive train is available to overcome a sudden torque demand as for instance needle penetration of a cross seam or the like.

Preferably at least one of the coil spring 30- or the annular member 40 is formed of a non metallic resilient material. As illustrated in the drawing, a metallic coil spring 30 is. employed and the annular member 40 is formed preferably of a synthetic plastic as for instance polyvinyl. With this arrangement objectionable noise incident to contact between the spring and the member 40 is obviated.

Having thus described the nature of the invention, what I claim herein is:

1. The combination of a sewing machine having a drive shaft, a gear wheel loosely journaled on said sewing machine drive shaft, an electric motor operatively connected to rotate said gear wheel, and a handwheel fast on said sewing machine drive shaft adjacent to said gear Wheel, power transmission means between said gear wheel and said handwheel comprising a coil spring formed with convolutions disposed substantially concentric about said sewing machine drive shaft, means securing one extremity of said coil spring to said handwheel and the other extremity to said gear wheel and a resilient annular abutment member having a peripheral spring engaging surface disposed on said drive shaft internally of the convolutions of said coil spring, said annular abutment member having a slight clearance under normal torque operating conditions with respect to the unflexed coils so that upon the application of additional torque, the coils of said spring will flex to a small uninhibited deflection and upon the application of increased torque, further deflection of the coil spring will be resisted by engagement of said coils with the surface of the annular abutment member.

2. In a device as set forth in claim 1 wherein said annular abutment member is formed of polyvinyl.

References Cited UNITED STATES PATENTS 1,548,458 8/1925 Grieb. 1,549,234 8/1925 Tomlin 64-27 1,935,683 11/1933 Wemp 64-27 2,332,859 10/ 1943 Kreissig et al. 64-27 2,863,411 12/ 1958 Peets i 112-220 3,224,398 12/1965 Greulich 112-220 JORDAN FRANKLIN, Primary Examiner. H. HAMPTON HUNTER, Assistant Examiner. 

